U.S. patent application number 13/994878 was filed with the patent office on 2013-12-19 for method for setting the clamping force applied by a parking brake.
The applicant listed for this patent is Frank Baehrle-Miller, Ulrike Mueller, Tobias Putzer, Matthias Schanzenbach. Invention is credited to Frank Baehrle-Miller, Ulrike Mueller, Tobias Putzer, Matthias Schanzenbach.
Application Number | 20130338896 13/994878 |
Document ID | / |
Family ID | 45217544 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130338896 |
Kind Code |
A1 |
Baehrle-Miller; Frank ; et
al. |
December 19, 2013 |
METHOD FOR SETTING THE CLAMPING FORCE APPLIED BY A PARKING
BRAKE
Abstract
In a method for setting the clamping force applied by a parking
brake, an electromechanical clamping force portion is set in an
electromechanical brake device, and an auxiliary clamping force is
set in an auxiliary brake device. A parameter of the electric
actuator is regulated to a defined value, while a state variable of
the auxiliary brake device, which determines the auxiliary clamping
force, is simultaneously set to a setpoint value without feedback
control.
Inventors: |
Baehrle-Miller; Frank;
(Schoenaich, DE) ; Schanzenbach; Matthias;
(Eberstadt, DE) ; Putzer; Tobias; (Bad
Friedrichshall, DE) ; Mueller; Ulrike; (Grossbottwar,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Baehrle-Miller; Frank
Schanzenbach; Matthias
Putzer; Tobias
Mueller; Ulrike |
Schoenaich
Eberstadt
Bad Friedrichshall
Grossbottwar |
|
DE
DE
DE
DE |
|
|
Family ID: |
45217544 |
Appl. No.: |
13/994878 |
Filed: |
December 5, 2011 |
PCT Filed: |
December 5, 2011 |
PCT NO: |
PCT/EP2011/071772 |
371 Date: |
August 29, 2013 |
Current U.S.
Class: |
701/70 |
Current CPC
Class: |
B60T 7/045 20130101;
B60T 8/17 20130101; B60T 13/741 20130101; B60T 13/588 20130101;
B60T 7/107 20130101; B60T 7/042 20130101 |
Class at
Publication: |
701/70 |
International
Class: |
B60T 8/17 20060101
B60T008/17 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2010 |
DE |
10 2010 063 345.3 |
Claims
1-14. (canceled)
15. A method for setting a clamping force applied by a parking
brake which includes an electromechanical brake device having an
electric actuator for generating an electromechanical clamping
force, and an auxiliary brake device which may be additionally
activated, for generating an auxiliary clamping force, the method
comprising: regulating a parameter of the electric actuator to a
defined value; and simultaneously setting a state variable of the
auxiliary brake device which determines the auxiliary clamping
force to a setpoint value without feedback control.
16. The method as recited in claim 15, wherein current applied to
the actuator is regulated as a parameter.
17. The method as recited in claim 15, wherein the clamping force
generated by the actuator is regulated as a parameter.
18. The method as recited in claim 15, wherein the auxiliary
clamping force of the auxiliary brake device is activated when a
state variable of the actuator lies outside a defined value
range.
19. The method as recited in claim 18, wherein the auxiliary
clamping force of the auxiliary brake device is activated when the
parameter of the actuator to be regulated or a variable correlating
therewith exceeds a threshold value.
20. The method as recited in claim 15, wherein the state variable
of the auxiliary brake device is provided as a time-dependent
curve, and a value of the state variable corresponding to the
instantaneous point in time is set.
21. The method as recited in claim 20, wherein the parameters
determining the curve are permanently predefined.
22. The method as recited in claim 20, wherein the parameters
determining the curve are determined as a function of parameters or
state variables of the electric actuator.
23. The method as recited in claim 22, wherein the parameters
determining the curve are adapted in the event of a loss in
functional performance or a defect in at least one of the electric
actuator and the auxiliary brake device.
24. The method as recited in claim 15, wherein the state variable
of the auxiliary brake device has a ramp-like increase until a
maximum value is reached.
25. The method as recited in claim 15, wherein the auxiliary brake
device is a hydraulic vehicle brake, and the state variable is the
hydraulic pressure.
26. The method as recited in claim 15, wherein the electric
actuator of the electromechanical brake device an electric brake
motor whose rotational speed is regulated with the aid of the
current.
27. A regulating or control unit for setting a clamping force
applied by a parking brake which includes an electromechanical
brake device having an electric actuator for generating an
electromechanical clamping force, and may be additionally activated
for generating an auxiliary clamping force, the unit configured to
regulate a parameter of the electric actuator to a defined value,
and simultaneously set a state variable of the auxiliary braking
device which determines the auxiliary clamping force to a setpoint
value without feedback control.
28. A parking brake in a vehicle, comprising: an electromechanical
brake device having an electric actuator for generating an
electromechanical clamping force; an auxiliary brake device which
may be additionally activated for generating an auxiliary clamping
force; and a regulating or control unit for setting a clamping
force applied by a parking brake including the electromechanical
brake device and the auxiliary brake device, the unit configured to
regulate a parameter of the electric actuator to a defined value,
and simultaneously set a state variable of the auxiliary braking
device which determines the auxiliary clamping force to a setpoint
value without feedback control.
Description
FIELD
[0001] The present invention relates to a method for setting the
clamping force applied by a parking brake in a vehicle.
BACKGROUND INFORMATION
[0002] An electromechanical parking brake is described in German
Patent No. DE 103 61 042 B3, which has an electric brake motor as
an actuator whose rotational movement is converted into an axial
actuating movement of a brake piston. The brake piston is the
carrier of a brake pad which is pressed against the end face of a
brake disk. The amount of clamping force is set by energizing the
brake motor.
[0003] Electromechanical parking brakes are also described which
interact with a hydraulic brake device, whereby the pressure of the
hydraulic brake device is applied to the brake piston adjusted by
the brake motor. The total clamping force in this case includes an
electromotively generated portion and a hydraulically generated
portion. When providing the clamping force, a noise development may
occur which is caused by the pump motor of the hydraulic brake
device which generates the necessary hydraulic pressure.
SUMMARY
[0004] An object of the present invention is to provide the
necessary clamping force in a parking brake of a vehicle which
includes an electromechanical brake device and an auxiliary brake
device, using simple measures and maintaining a high level of user
comfort.
[0005] An example method according to the present invention is used
in a parking brake in vehicles, the parking brake being provided
with an electromechanical brake device and an activatable brake
device. The electromechanical brake device of the parking brake
includes an electrically operable actuator which may be used to
generate an electromechanical clamping force. To hold the vehicle
at a standstill, a clamping force is generated with the aid of the
electromechanical brake device.
[0006] In addition, the auxiliary brake device may be activated,
for example in situations in which the electromechanical clamping
force is insufficient to stop the vehicle as safely as necessary.
It is also possible to activate the auxiliary brake device to
relieve the electromechanical brake device, since the
electromechanical portion of the clamping force may be reduced
accordingly when the auxiliary brake device is activated.
[0007] The electric actuator is preferably an electric brake motor
whose rotational movement is converted into an axial actuating
movement of a brake piston. The brake piston is the carrier of a
brake pad which is pressed against the end face of a brake
disk.
[0008] In principle, however, another electric actuator for
generating the electromechanical clamping force is possible, for
example an electromagnetic actuator.
[0009] The auxiliary brake device is preferably designed as a
hydraulic brake device whose hydraulic pressure is used to generate
an additional, supplementary clamping force. For example, the
hydraulic pressure may be additionally applied to the brake piston
which is adjusted by the electromechanical brake device, so that
the total clamping force includes an electromechanical portion and
a hydraulic portion.
[0010] In generating the electromechanical clamping force, a
parameter of the electric actuator is regulated to a defined value;
for example, an electric parameter such as the current in the
actuator or the force generated by the actuator is regulated. At
the same time, the auxiliary clamping force is set to a setpoint
value with the aid of an assigned state variable of the auxiliary
brake device, without regulation by a feedback loop but solely on
the basis of a control without feedback. In the example method
according to the present invention, a regulation for the
electromechanical brake device and a control of the auxiliary brake
device act together. This ensures, on the one hand, a sufficiently
accurate setting of a total clamping force which includes an
electromechanical portion and a portion of the auxiliary brake
device. Regulating the electromechanical brake device allows the
total clamping force to be set precisely.
[0011] On the other hand, the method may easily be implemented and
carried out on the basis of the unregulated control of the
auxiliary brake device, since no feedback loop is required for the
auxiliary brake device when setting the auxiliary clamping force.
The noise development is also reduced, since only a certain,
defined level for setting the auxiliary brake device must be
reached during the control, which may be achieved without
fluctuating or alternative state variables of the auxiliary brake
device. In the case of regulation, in contrast, a constantly
changing state variable of the auxiliary brake device must be taken
into account, which is associated with an unpleasant noise which
changes in pitch. In the preferred event that the auxiliary brake
device is a hydraulic brake device, in particular the regular
vehicle brake, the pump motor of the hydraulic brake device must be
regulated at a constantly changing rotational speed during
regulation for the purpose of generating the desired hydraulic
pressure. In the case of control according to the present
invention, in contrast, a certain, defined rotational speed curve
is applied to the pump motor, so that continuously changing
rotational speeds may be avoided.
[0012] Another advantage may be seen in the fact that the risk of a
tendency to oscillate due to feedback of the motor current of the
electric actuator is ruled out. Conversely, such a tendency to
oscillate may be present in parking brakes in which both the
electric brake motor and the hydraulic brake device interacting
with the brake motor are subjected to regulation. In the design
according to the present invention, the pump speed of the hydraulic
pump remains at least nearly constant, and the load on the
components and vehicle electrical system is reduced.
[0013] According to one advantageous embodiment, the current
applied to the actuator is regulated as an electric parameter on
the part of the electromechanical brake device. To achieve a
desired electromechanical clamping force, a certain current level
must be applied to the electric actuator. Additionally or
alternatively, the regulation takes place with the aid of the
clamping force generated by the actuator, in particular in a
further phase of the clamping operation.
[0014] The auxiliary clamping force generated in the auxiliary
brake device is advantageously activated during the clamping
operation of the electromechanical brake device. The achievement of
a defined value range of a state variable of the actuator may be
the trigger for the activation. For example, it is advantageous to
use the current which is applied to the electric actuator as a
criterion for activating the auxiliary brake device. If the current
exceeds a threshold value, support by the auxiliary brake device is
requested. The value range for the considered state variable may be
either permanently predefined or established as a function of
system variables, in particular state variables of the
electromechanical brake device and/or the auxiliary brake
device.
[0015] In addition or as an alternative to the consideration of the
current of the electric actuator, the auxiliary support may also be
activated upon dropping below a motor speed threshold. In this
case, which relates to the use of an electric brake motor in the
electromechanical brake device, the risk of the brake motor
stopping due to an excessively heavy load may be reduced with the
aid of the auxiliary clamping force support.
[0016] To control the auxiliary brake device to the desired value
of the auxiliary clamping force, a state variable of the auxiliary
brake device, which determines the clamping force, is
advantageously set to a value which is present as a function or a
characteristic curve. For example, the setpoint value of the state
variable may be present as a time-dependent or travel-dependent
curve, so that the state variable may be set accordingly at the
instantaneous point in time or for the instantaneous displacement
of the electromechanical actuator. If a hydraulic brake device is
used as the auxiliary brake device, the state variable is
advantageously the hydraulic pressure which is set to a
corresponding setpoint in an unregulated way, following the course
of the curve.
[0017] The parameters determining the course of the curve for the
state variable of the auxiliary brake device may be either
permanently predefined or established as a function of other state
variables or parameters, in particular they may be dependent on
state variables or parameters of the electric actuator. The course
of the curve of the setpoint values for the state variable of the
auxiliary brake device is designed, for example, as a ramp which
ascends up to a defined maximum value. Both the gradient of the
ramp and the maximum value represent parameters which are either
permanently predefined or established as a function of other
variables of the parking brake during ongoing operation. For
example, it is possible to adapt the parameters determining the
course of the curve in the event of a loss in functional
performance or a defect in the electric actuator and/or the
auxiliary brake device. For example, if the brake motor as the
electric actuator of the electromechanical brake device is unable
to provide the requested clamping force, due to a power drop, an
adaptation of the setpoint curve for the auxiliary brake device may
compensate for the power drop, in particular by raising the
gradient in the ramp-like rise and/or by raising the maximum value.
Even if a defect occurs in the auxiliary brake device, for example
in the design as a hydraulic brake device, if air is present in the
hydraulic system, at least a partial compensation of the power drop
may be achieved by adapting the parameters of the setpoint
characteristic curve.
[0018] The example method according to the present invention may
run in a regulating or control unit in the vehicle, which may be
part of the parking brake system.
[0019] Additional advantages and advantageous embodiments are
described below and shown in the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a section of an electromechanical parking brake
for a vehicle, in which the clamping force is generated with the
aid of an electric brake motor.
[0021] FIG. 2 shows a diagram of the time-dependent curve of the
current, the voltage and the motor speed as well as the hydraulic
pressure and the total clamping force during a clamping operation
of the parking brake.
[0022] FIG. 3 shows a diagram of the curve of a current threshold
value as a function of the voltage.
[0023] FIG. 4 shows a diagram of the curve of the setpoint pressure
for the hydraulic brake device as a function of time.
[0024] FIG. 5 shows a flow chart of the individual method steps for
carrying out the method for setting the parking brake.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0025] FIG. 1 shows an electromechanical parking brake 1 for
holding a vehicle at a standstill. Parking brake 1 includes a brake
caliper 2 having a clamp 9 which grips a brake disk 10. As the
actuator, parking brake 1 has an electric motor as brake motor 3,
which rotationally drives a spindle 4 on which a spindle component
5 is rotatably mounted. When spindle 4 rotates, spindle component 5
is axially adjusted. Spindle component 5 moves within a brake
piston 6, which is the carrier of a brake pad 7 which is pressed
against brake disk 10 by brake piston 6. Another brake pad 8, which
is fixedly held in place on clamp 9, is located on the opposite
side of brake disk 10.
[0026] During a rotational movement of spindle 4, spindle component
5 may move axially forward within brake piston 6 in the direction
of brake disk 10 or, in a reversed rotational movement of spindle
4, it may move axially backward until it reaches a stop 11. To
generate a clamping force, spindle component 5 strikes the inner
end face of brake piston 6, whereby axially movable brake piston 6,
which is mounted in parking brake 1, is pressed against the facing
end face of brake disk 10 by brake pad 7.
[0027] If necessary, the parking brake may be supported by a
hydraulic vehicle brake in such a way that the clamping force
includes an electromotive portion and a hydraulic portion. During
the hydraulic support, pressurized hydraulic fluid is applied to
the back of brake piston 6 facing the brake motor.
[0028] FIG. 2 shows the time curve of different operating variables
of a parking brake during a clamping operation of the brake. The
clamping operation may be largely divided into four phases:
[0029] At the beginning of a phase I, a clamping request is
detected at point in time t1, and electric brake motor 3 is
activated. Upon activation of brake motor 3, a starting current
peak is detectable. Current I of the brake motor then drops during
the further progression until a no-load current sets in at point in
time t2 at the end of phase I. Rotational speed n of the brake
motor increases during phase I, and the brake motor is accelerated.
At the end of phase I, rotational speed n of the brake motor
reaches an idling speed at point in time t2. Voltage U of the brake
motor also increases, and a no-load voltage sets in at the end of
phase I. The rotation of a spindle causes a nut or the spindle
component to move in the direction of the brake piston of the wheel
brake. Since the nut is not yet in contact with the piston head,
clamping force F is initially still zero. Pressure p of a hydraulic
pump of the hydraulic brake device is also zero during this
phase.
[0030] Phase II between points in time t2 and t3 marks the idling
phase in which a no-load current, a no-load voltage and an idling
speed set in. The clamping force of the wheel brake remains zero
during this phase, since the nut is not yet in contact with the
piston head. Pressure p in the hydraulic brake device continues to
be equal to zero.
[0031] The buildup of force takes place in phase III between points
in time t3 and t4. The nut is in contact with the piston head, and
the piston is pressed against the brake disk by the rotation of the
spindle. Current I of the brake motor increases. During this phase,
voltage U of the brake motor drops slightly from the level of the
no-load voltage, due to the load on the brake motor. Rotational
speed n of the brake motor also decreases as the clamping force
buildup increases. Shortly before the predefined target clamping
force is reached, the hydraulic pump of the hydraulic brake device
is activated, and a hydraulic pressure p builds up. The target
clamping force may have, for example, a value which is close to the
maximum clamping force of the brake motor.
[0032] Phase IV between points in time t4 and t5 begins when the
target clamping force is reached. During this phase, both brake
systems are active, and the electric brake device is supported by
the hydraulic brake device. Total clamping force F includes a
portion of the electric brake motor and a portion of the hydraulic
brake device. Current I of the brake motor is limited to a maximum
current in phase IV. Hydraulic brake pressure p continues to
increase until a predefined total clamping force has been reached.
The brake motor and the pump motor of the hydraulic brake device
are then deactivated. As a result, hydraulic pressure p, current I,
voltage U and rotational speed n of the brake motor drop to zero.
Total clamping force F is maintained in the process.
[0033] The hydraulic brake device is not activated again until
phase IV, so that the buildup of hydraulic pressure p, which has
reached its maximum value at the end of phase IV, i.e., at point in
time t5, begins at point in time t4.
[0034] However, the point in time of the pressure support by the
hydraulic brake device is not absolutely linked to point in time
t4, at which phase IV begins. The point in time of the hydraulic
support is advantageously established as a function of a parameter
of the electric brake motor, in particular the current of the brake
motor. For this purpose, a check is carried out to determine
whether current I of the brake motor exceeds an assigned threshold
value I.sub.lim. If this is the case, the hydraulic pressure
support begins.
[0035] As shown in FIG. 3, current threshold value I.sub.lim may be
established as a function of voltage U. Threshold value I.sub.lim
thus does not represent a constant variable but is adapted as a
function of motor voltage U. The function curve according to FIG. 3
is designed as a ramp which reaches a maximum value at a certain
voltage value. Due to the adaptation of current threshold value
I.sub.lim, the triggering of phase IV may be adapted to the
operating conditions of the brake motor. The adaptation of the
threshold value is necessary, since the maximum possible motor
current decreases proportionately to the motor voltage, and the
maximum possible motor torque in the parking brake is thus also
available only to a reduced degree.
[0036] However, it is also possible, in principle, to predefine
current threshold value I.sub.lim as a fixed, constant
variable.
[0037] FIG. 4 shows the pressure curve of hydraulic pressure p as a
function of time. The pressure curve is predefined as a setpoint
curve for setting the hydraulic brake device. The setting is
carried out only in a controlled way without a feedback loop; only
a parameter of the electric brake motor is regulated to a setpoint
value. The regulation of the brake motor is carried out with the
aid of the current in phase III. In phase IV, in contrast, the
force generated by the brake motor is regulated with the aid of the
distance traveled and the rigidity of the brake caliper.
[0038] As shown in FIG. 4, the setpoint curve of pressure p is
designed as a ramp with a gradient dp/dt, which reaches its maximum
value at p.sub.max. Gradient dp/dt as well as maximum value
p.sub.max represent parameters which are either permanently
predefined or are determined as a function of state variables or
parameters of the electromechanical brake device and/or of the
hydraulic brake device. For example, a higher gradient and a higher
maximum value may be selected over the course of setpoint curve p,
if a power loss occurs in the electromechanical brake device.
[0039] FIG. 5 shows a flow chart of individual method steps for
setting the total clamping force in the parking brake. The flow
chart begins in force increasing phase 3 at point in time t3
according to first method step 20. Step 21 is used to predefine a
clamping force as the target clamping force, which may be used to
hold the vehicle in place on an inclined surface having a 30%
gradient.
[0040] Further method steps 22 and 23 correspond to force
increasing phase III. According to step 22, the trigger criterion
for starting the hydraulic clamping force support is ascertained.
For this purpose, current threshold value I.sub.lim is determined
according to the context illustrated in FIG. 3. A query of whether
instantaneous motor current I exceeds current threshold value
I.sub.lim is carried out in subsequent method step 23. If this is
not the case, the method goes back, following the no branch ("N"),
and another check of whether motor current I has exceeded threshold
value I.sub.lim is carried out at regular intervals.
[0041] When motor current I exceeds threshold value I.sub.lim, the
method follows the yes branch ("Y") to next method step 24, which,
along with subsequent method step 25, is assigned to phase IV (FIG.
2). In method step 24, a controlled pressure ramp is started
according to the diagram shown in FIG. 4, and the hydraulic
pressure in the hydraulic brake device is increased according to
the predefined ramp function shown in FIG. 4. In next step 25, a
query is carried out of whether the total clamping force, which
includes the electromotive portion and the hydraulic portion, has
been reached. If this is not the case, the method follows the no
branch back to the query, and the query is restarted at regular
intervals. However, if the total clamping force is reached, the
method follows the yes branch to next method step 26, which marks
the end of the clamping operation in the parking brake. Point in
time t5 (FIG. 2) is reached in method step 26.
* * * * *